There is Patent Literature 1 as a background art of the technical field. The patent publication discloses that “to suitably decide a priority order in the case of using a bus between devices and to sufficiently transfer data between devices even when any device is connected to the bus in an information processor connecting plural devices on the same bus. When an existent device 102 and an extended device 105 respectively request the use of a bus 101 to a bus arbitrating means 110 through bus use request signals 103 and 113, the bus arbitrating means 110 selects either the existent device 102 or the extended device 105 and applies the use right of the bus 101 in accordance with the priority order decided by a priority order deciding means 109 based on device information obtained from an existent device information storing means 104 and an extended device information storing means 107 (see Abstract).